This invention relates to low-molecular weight urethanediols obtained by a reaction of methylenebis(4-phenyl isocyanate) with 1,4-butanediol and to their use as components in polyurethane formulation either as "hard segment" components or as curing agents.
Methylenebis(4-phenyl isocyanate), sometimes referred to as MDI throughout this disclosure, is a known commercial starting material for the preparation of polyurethanes having desirable physical properties. While such MDI-based prior art polyurethanes have found numerous applications in molded articles and coatings, they were not adequate in those applications where high hardness was desired, for example, in floor finishes. It had been a common practice in the past to use polyamines, especially aromatic polyamines, to cure isocyanate-terminated prepolymers to polyurethane products of high hardness, but this practice has more recently become less acceptable because of the potential toxicity of amine-based curing agents as well as lower hydrolytic stability of polyurethanes containing urea groups. On the other hand, diol- or polyol-based cures were not capable of providing the desired high hardness, except when a large amount of free MDI was present in the isocyanate-terminated prepolymer. However, this resulted in a very vigorous reaction accompanied by large heat evolution, which caused cured, fabricated articles (especially those of larger thicknesses) to be nonhomogeneous and thus frequently unsatisfactory. It, therefore, is an object of the present invention to provide diol-based polyurethane curing agents which would give cured products of high hardness.